This application claims the priority of 199 55 525.7, filed in Germany, Nov. 18, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for condensing a fiber strand which travels through a condensing zone in an untwisted state after leaving a drafting unit, and in which condensing zone the fiber strand, disposed on the outside of an air-permeable, circling transport belt, is transported over a suction slit which is arranged in a stationary sliding surface which guides the inner side of the transport belt, which sliding surface is formed by means of the outer contour of a hollow body connected to a vacuum.
An apparatus for pneumatic condensing of this type is disclosed in German published patent application 198 46 268 (corresponding U.S. Pat. No. 6,108,873). For the pneumatic condensing of a fiber strand leaving a drafting unit it is important that the fiber strand is transported in the condensing zone disposed on an air-permeable transport element while still in a twist-free state and having fibers essentially disposed parallel to one another, and that in the condensing zone an air stream is generated which flows through the transport element, said air stream thus determining the degree of condensing by means of its width and/or direction and, positioning the fibers diagonally to the transport direction so that the fiber strand is bundled or condensed. In the case of such a condensed fiber strand, no spinning triangle occurs before the twist is imparted, so that the thread produced therefrom is more even, more tear resistant and less hairy
In practice it has been shown that in the case of pneumatic condensing a certain amount of fiber fly occurs, which can in time block the perforations of the transport belt, which impairs the condensing effect. When the desired condensing effect does not take place, this can result in the finished cloth having a so-called Moire effect, which can render the product a reject. It must therefore be ensured that the condensing effect is not impaired by blockage of the perforations at the individual spinning stations.
It is an object of the present invention to ensure that the perforations of the transport belt do not become blocked and that the condensing effect is not impaired.
This object has been achieved in accordance with the present invention in that the hollow body comprises a pressurized chamber, which comprises, in an area facing away from the suction slit, at least one air outlet opening directed against the inner side of the transport belt.
The air outlet opening, of which there is at least one, should be located where outcoming pressurized air is not harmful for the condensing process, that is, in an area facing away from the suction slit. A light, constant pressure is sufficient, which continuously "expels" the fiber fly. Because of the effective width of the transport belt, it is possible to arrange a plurality of air outlet openings in a row adjacent to one another.
In an advantageous embodiment of the present invention, the at least one air outlet opening runs into a hollow space, which is defined on one side by the outer contour of the hollow body and on the other side by the inner side of the transport belt. Thus the light pressure is effective over the entire effective width of the transport belt despite the presence of only one air outlet opening. In addition, because of the occurring hollow space, the fiber fly can be more easily removed from the transport belt. Fiber fly can be pressed from the inside to the outside of the transport belt and can leave the transport belt at a place which is not detrimental to the condensing process.
It is provided that in the area of the hollow space a roller of the front roller pair of the drafting unit is disposed on the outer side of the transport belt. Hereby the driven front bottom roller is advantageously used, whose rotational direction is the opposite direction to the running direction of the transport belt and thus also removes fiber fly mechanically from the outside of the transport belt. The above mentioned hollow space is hereby adapted to the contour of the disposed roller.
In further embodiments of the present invention, the hollow space is covered in running direction of the transport belt by a bordering surface, which is disposed with a scraping edge closely to the inner side of the transport belt. This prevents any air from flowing off to the condensing zone where it could be detrimental. In addition, a mechanical cleaning on the inner side of the transport belt takes place.
It has proven to be practical when the bordering surface is arranged at an extension comprising the suction slit, which extension, together with a hollow profile connected to a vacuum source, forms the hollow body. This arrangement is not only practical as regards the manufacture of the components, but also the extension can be limited to that area of the hollow body where the transport belt is guided and where wear is most likely to be expected. The extension is therefore advantageously made of ceramic.
The hollow space is connected to the atmosphere in the opposite direction to the running direction of the transport belt, so that the air can flow there where it is absolutely harmless for the spinning process, namely through the perforations of the transport belt to the outside.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings.